The present invention relates to a rubber composition for a tire and a tire using the same.
In tread rubber of high performance tires such as racing tires, usually both high gripping performance and abrasion resistance are required.
Conventionally, as rubber compositions for a tire having high gripping performance, known are a rubber composition containing styrene-butadiene copolymer rubber (SBR) having a high glass transition temperature (Tg) as the rubber component; a rubber composition in which process oil is substituted with an equivalent amount of resin having a high softening point which is added to the rubber component; a rubber composition in which a large amount of a softening agent or carbon black is added; and a rubber composition in which a combination of SBR, resin having a high softening point and a softening agent or carbon black is compounded. However, a rubber composition in which SBR having high Tg is used has the problem that temperature dependency is large and the influence of temperature change on performance becomes large. Furthermore, in the case that carbon black having small particle size or a large amount of a softening agent is used, dispersability of carbon black is poor and abrasion resistance decreases.
In order to solve the above problems, a rubber composition containing low molecular weight styrene-butadiene copolymer has been suggested (see JP-A-63-101440). However, because low molecular weight styrene-butadiene copolymer has crosslinkable double bonds, part of the low molecular weight component crosslinks with the matrix rubber component and is introduced into the matrix. As a result, there is the problem that hysteresis loss cannot sufficiently be suppressed. Also, in the case that double bonds are made into saturated bonds by hydrogenation in order to prevent the low molecular weight component from being introduced into the matrix by crosslinking, compatibility with the matrix decreases significantly. Consequently, problems occur such as decrease in destruction resistance properties and bleeding of the low molecular weight component.
Also, in order to improve gripping performance on wet road surfaces (wet grip performance), a rubber composition containing halogenated butyl rubber or halogenide of a copolymer of isobutylene and p-methylstyrene and silica has been suggested (see JP-A-2000-204198). However, the balance of gripping performance and abrasion resistance is insufficient.
In the same way, in order to improve wet grip performance, a rubber composition containing hydrogenated SBR and silica is suggested (see WO 96/05250). However, wet grip performance cannot sufficiently be improved.
Furthermore, a rubber composition containing liquid polybutadiene has been suggested (JP-A-2000-273245). However, although gripping performance improves, abrasion resistance decreases.